Laser processing of 3D-plastic components - the best answer may be a 'Laser Robot'

Today's plastic components, especially in the automotive industry, are becoming more and more complex. The enormous possibilities that these plastic materials offer have been recognized by the designer, and are being used more than ever before. This has created components that can no longer be processed economically with conventional cutting methods. Furthermore, in recent years the rate of product change and face lifting has in-creased dramatically. The result is that rigid production installations are not practical due to high change over costs. The best solution today may be flexible automation with ro-bots.

From planning to the complete cell
For a successful execution of a laser application it is important that the complete cell is delivered from a single source under sole responsibility. Planning, designing, and manu-facturing of the turnkey installation ideally should be done in close cooperation with the end user. Reis Robotics is creating an extensive customer support function. The cus-tomer is involved from the beginning in the solution of the correct components, the right cutting process based upon careful study of the specific task, through the delivery, accep-tance and installation of the completed system. Reis Robotics provides the total process technology knowledge so that even complex applications can be accomplished in partner-ship with the customer.

The core piece of a laser cell from Reis Robotics is the laser robot. The basic model con-sists of a 5-axes Reis RV-16 standard robot available in two sizes. The robot is especially equipped with a CO2-Laser. Depending on the part size and the cutting task, a custom-ized cell is planned consisting of a material handling function, a robot work envelope, and a filter function. The cells are of modular design for faster on site assembly. Depending on the cycle time, the part size, the available space, and the material flow, the best cell arrangement is determined using either double slide tables or a rotary table. The slide table provides shorter material handling times.

Reis RV-16L Laser Robot. The only system in the world with the laser beam guided through the robot arm. This patented feature provides unlimited freedom of motion with maximum safety of the beam.

Robot with integrated beam guiding
Reis Robotics offers two different robots sizes dependent upon the power of the laser and the reach necessary to cut the part. The Reis Robot RV-16 handles a laser power range up to 150 watts and a reach radius of 1414mm. The Reis RV-16L can handle up to a 600-watt laser with a reach radius of 2300 mm.

Both robots are equipped with an integrated beam guiding and a mounted CO2-Laser. The mounting of the CO2-Laser on the robot ensures an extremely flexible and process-safe beam guiding system. The particularly compact mounting ensures short beam travel, un-limited freedom of movement of the robot, and a good accessibility to the components. The conventional problems with exterior beam guiding are eliminated.

The patented beam guiding was developed in cooperation with Thyssen-Laser-Technik located at Aachen. With the CO2-Laser mounted on axis 3, the emerging laser beam is guided with a deviation mirror and a beam offset element in the head axis. From there, the totally enclosed laser beam is steered into the narrow cutting optics. Adjustment of the mirrors is accomplished by means of a harmless visible diode laser beam from a separate source. This allows easy programming and mirror adjustment. In addition to the deviation mirrors, the axis head is also equipped with a nozzle that provides a process gas, which eliminates contamination from accumulating on the lens while assisting in the cutting process.

Robust and light CO2-Laser
Lasers from 50 watts to approximately 600 watts are used. These lasers are outstanding due to their low weight and small size. They are extremely robust and resistant to the high acceleration forces caused by the robot movement. The smoothest point in the movement range of the robot was chosen in mounting the laser to axis 3.

The high quality of the laser combined with a very small focal point and high beam energy produces an excellent cutting process. The 10.6 µm wavelength of the CO2-Laser is ideally suited for cutting plastic materials or textiles. The laser power can be controlled with the robot programs. This allows a continuous adjustment of the laser power, even during robot movement, from maximum down to nearly 0 Watts.

In order to ensure the highest possible safety, the lasers are equipped with shutters, which prevent emission of the beam when the robot is stopped. This shutter also closes imme-diately in case of an 'E-stop'. In addition to the proper laser resonator on axis 3, a power pack, a control unit and a cooling unit are still required which are not attached to the robot.

Component fixture
The component fixture is a very important part of the laser cell. The fixture must hold the part consistently every time. It must also be designed for quick and easy part exchange to provide the lowest cycle time. Reis Robotics manufacturers milled aluminum contour fix-tures based on model parts. This ensures high dimensional accuracy and true confor-mance to the component.

CAD-data do not produce enough accuracy in milled fixtures because they do not reflect the high dimensional irregularities that occur in real parts. This is due to different shrink-age and variations in other parameters in the plastics. The fixture external surfaces are sand blasted to minimize reflection of the laser beam. The components are clamped with suction units or pressure clamping devices.

Filter technique
Another important aspect of the component fixture is the channel through which cutting gases are extracted. Special care must be taken to prevent contamination of the parts or the fixture.

The gases produced during laser cutting must be properly cleaned and filtered. Suction devices over the individual fixtures and in the ceiling of the laser cell remove these gases. The valves that regulate these suction units are controlled by the program to create suc-tion only in the cutting area.

For inorganic components such as talcum, a pre-filter is required to remove the talcum. The remaining cutting gases are sent through a Katasorb sinter lamella filter with a closed cleaning stage. Selection of the correct filter and elements is made based upon the exact material that is to be cut. Air from the filter should be exhausted outside the building to avoid contamination if the filter should fail.

Programming with the 6DMouse
The entire preliminary program including the cycle, the fixturing, the filter system, and the robot is performed at Reis Robotics. This initial program, including teaching the cutting path, is done with the Teach Pendant in the 'Teach-In' mode. For an optimum program-ming of complex parts, a Spline interpolation is used.

In addition, the operator can use the exclusive Reis 6D-Mouse mounted to the head axis of the robot to manually guide the robot along the path. A separate software function called 'RobAssist' permits the integration of special parameters such as: 'Laser on - off', 'process gas on - off, 'power control', 'etc. to be introduced into the program by pushing specially marked buttons. These macros are stored in the main memory of the robot con-troller and can be called up as often as needed and inserted into the program to yield a clear and simple program.

The greatest advantage of the robot in cutting of plastic materials is its flexibility in adapt-ing to any shape. New components can be programmed and manufactured very quickly and economically. Modifications to parts can also be quickly accommodated. Particularly in the automotive industry it is often necessary to modify the programs in the range of tenths of millimeters due to tolerance changes or add-on pieces.

Safety technique
The total cell consists of a closed system with parts presented by a transfer system. The access doors have interlock switches. Large windows can be integrated in the laser area for observation of the operation. These windows are double glazed to prevent breaking.

Prospective outlook
In the future, laser technology will be increasingly used for cutting plastic materials. More powerful lasers with higher cutting speeds will make this process even more economical. A dramatic increase in the cutting speed will soon be available with the addition of a 600-watt laser to the robot cell. The continued improvement in beam quality and cutting speeds will bring more progress to laser cutting and laser welding of plastic materials.

Advantages of the laser cutting technique

The laser process is excellent for cutting plastics due to the high quality of the cut edge. In cutting textile parts, the edges are sealed which prevents fraying.